Species&colon; Skyros wall lizards (Podarcis gaigeae)Habitat&colon; A small number of Greek islands on the Aegean Sea

A sunny Greek island bursting with food and without a predator in sight sounds like heaven. For young lizards, the reality is more of a nightmare – full of super-sized cannibals.

Advertisement

Thanks to the buffet of fish scraps and bird poo provided by the resident seagull colony, living conditions for wall lizards on the tiny island of Diavates, in Greece’s Aegean Sea, are good.

So good in fact that adults balloon to up to three times their normal weight. But the population is also much denser, making competition for mates and meals fierce. And when the going gets tough, it is the weakest that become targets.

“Cannibalising youngsters is an effective way to get rid of future rivals and at the same time get a nutritious meal,” says Panayiotis Pafilis from the University of Athens in Greece. Dwarfed by the huge adults, juveniles don’t stand a chance. This is not a great place to grow up, although it’s a great one to retire to if you’re lizard.

Just 4 kilometres away on the larger island of Skyros, there are plenty of predatory snakes, mammals and birds to keep lizard numbers down. Here, the adult and juvenile lizards live in relative harmony.

On Skyros, the wall lizards still attack youngsters – as many lizard species do – but this usually involves nibbling off a stray toe or tail. Rarely do they kill and swallow their victim whole as the Diavates giants do.

Individual cases of cannibalism in lizards have been seen in the US and Serbia. But cannibalism is infrequent because competition for resources has to be fierce to make the tiring practice worthwhile.

What really strikes Pafilis as extraordinary is the sheer frequency of attacks on Diavates. Previous research found that Diavates lizards were some 20 times more likely to have juvenile body parts in their stomach than lizards on Skyros.

Pafilis and his colleagues decided to study this behaviour in real time – placing a hungry adult in an enclosure with a single youngster. What they saw confirmed their belief that cannibalism is not just for fringe deviants. It may well be the norm on this island.

Over two-thirds of the Diavates lizards attacked juveniles, compared with 17 per cent of Skyros reptiles. The waiting period before attacking was also nearly six times shorter for the Diavates animals. The urge to eat each other is so strong in giant wall lizards that they even tried their luck on other fully grown adults.

Interestingly, females seem to have more conventional food preferences. It is possible that killing a youngster is beyond their physical abilities&colon; they are smaller and may have weaker jaws.

In the dog eat dog world of Diavates, cannibalism makes sense. However, Pafilis is puzzled by how it affects the males’ chances of passing on their genes to the next generation. Eating their own offspring obviously doesn’t help this basic desire, so it may be that they have some way of recognising their kin. That question, he says, is next on the list for his research team.